Brakes are an energy-absorbing mechanism that converts vehicle movement into heat while stopping the rotation of the wheels.
All braking systems are designed to reduce the speed and stop a moving vehicle and to keep it from moving if the vehicle is stationary.
Drum Brakes
Drum brakes use friction material called shoes. Drum brakes are not as efficient as disc brakes at dissipating heat. Drum brakes can apply more stopping power for the given amount of force applied to the brake pedal.
Disc Brakes
used on the front of most vehicles they operate by squeezing brake pads on both sides of a rotor or disc that is attached to a wheel
Weight Transfer During Braking
Inertia in the form of weight transfer plays a major part in braking performance, Newton’s First law of motion states that an object in motion will remain in motion unless acted upon by an outside force. The brakes are that outside force and when braking the wheels and tires slow immediately. The rest of the vehicle attempts to stay in motion, therefore the weight transfers to the front wheels.
Friction
friction is the force between two objects in contact with each othe
Brake Fluid
Brake fluid is the life source of the braking system. without brake fluid the brakes would not work. since fluid is non compressible, it acts as a hydraulic. brake fluid has a high boiling point since the brakes get to a temperatrure of 1300 degrees F and get as high as 1800 degrees F. brake fluid also has a high freezing point.
DOT Brake Fluid Specs.
The Department of Transportation has established brake fluid standards shown in the table.
Some French-built and British designed cars use HSMO (Hydraulic System Mineral Oil) as part of their hydraulic control systems. They use a hydraulic pump to pressurize the HSMO for use in suspension leveling and braking systems.
Brake Fluid Testing
Check proper level after inspecting entire brake system for worn pads or shoes and leaks; Check color/condition should be clear or amber; Use test strips for copper ions, compare test strip to color on package;Or, an electronic boiling point tester is submerged into the master cylinder fluid, push the button and the boiling temperature will be displayed. For contamination, fill a styrofoam cup with water, place a teaspoon of brake fluid and it should completely dissolve. Petroleum or mineral oil fluids will float to the surface and retain their color. Contaminated brake fluid must be drained, flushed, and replace all rubber components.
Brake Fluid Disposal
Brake fluid should be disposed of just like petroilime based products and not just dumped down the drain or dumped outside.
Brake lining Composition: A molded resin friction material composition for automobiles or the like. This composition contains as base fibers chopped glass fibers and pulped polyamide fibers in a given compounding ratio. This composition enables to produce brake lining having a high friction coefficient, a low wear ratio, and an improved fade. The fade can be further improved by adding cryolite powder and zirconium oxide powder to the composition.
Semi-Metallic Friction Material Composition
Lining Edge Codes
A set of numbers and letters used to identify the brake lining materials. The first group is a series of letters that identify the manufacturer of the lining. The second group is a set of numbers or letters or both that identify the compound of the lining. The last group is two letters that identify the coefficient of friction. The first letter is the coefficient of the lining when the brakes are cold and the second letter represents the coefficient of the lining when the breaks are hot.
The Dangers of Exposure to Asbestos The inhalation of asbestos fibers by workers can cause serious diseases of the lungs and other organs that may not appear until years after the exposure has occurred. For instance, asbestosis can cause a buildup of scar-like tissue in the lungs and result in loss of lung function that often progresses to disability and death. Asbestos fibers associated with these health risks are too small to be seen with the naked eye, and smokers are at higher risk of developing some asbestos-related
diseases.
OSHA Standards Re: Asbestos
OSHA standards state that and vehicle service establishment that does either brake or clutch work must limit employee exposure to asbestos to less than .2 fibers per cubic centimeter
EPA Regulations of Asbestos
Asbestos is hazardous if it is air born and should be wet down before handling. Once wet down it can be treated the same as any other waste
Asbestos Handling Guidelines- Should treat all brake pads, shoes, and clutch disks, as if they contain asbestos
Antilock Brake System Operation
Brake Drums
Brake drums are made of cast iron or cast aluminum with a cast iron liner. The brake drum turns with the wheel it mounts on the hub or axlke and covers the rest of the brake assembly. Have ribs or fins on the outer edge to help dissapate heat.
Hard Spots
if brake temperatures get to hot impurities int he metal can be burned away altering the structure of the metal
“Machine to” vs. “Discard Dimension”
Most manufacturers recommend a minimum amount of material be available for wear. If the difference between the starting measurement and the finished machine to measurement is going to accede the recommended minimum material amount then the Drum or rotor should be discarded.
Measuring and Inspecting Brake Drums
Brake drums can be inspected visually and by feel. when inspecting brake drums, you should look for roughness, cracks, rust, deep gouges and scratches.
Machining Drums
when machining drums be sure that it is sitting straight on the machine. be sure to make a scratch mark to make sure the the drum is sitting straight. for your first cut be sure to take no less then .002 of an inch and no more of .004 of an inch. when done, take sand paper to scuff up the surface. remove the drum from the machine and wash it with soap and water, or brake clean.
Cast Iron Rotors
Disk brake rotors use cast gray iron at the area that contacts the friction pad. The heavier the rotor the more heat can be absorbed.
Aluminum Metal Matrix Composite Rotors
Made up of aluminum and 20% silicon carbide particulate. Aluminum composites combine the light weight and thermal conductivity of aluminum with the stiffness and wear resistance of a ceramic to creat a disc brake rotor with excellent heat dissipation and service life
Lateral Runout
Lateral runout, or total indicator runout, is side to side wobble of the rotor as it rotates on the spindle. May cause piston knockback which reduces drag when brakes are not applied. May have excessive brake pedal travel and front end vibration felt in the steering wheel. Severe runout may experience a pulsating brake pedal. Some causes of lateral runout are: Over tightening or unevenly tightening lug nuts; Extreme heat or rapid temperature variations; inaccurate machining: Max runout is .003"
Rotor Thickness (Parallelism)
Standard value
Limit
Disc rotor outer diameter
|| Disc rotor thickness A mm (in) || 15" || 24 (0.94) || 22 (0.87) || 277 (10.91) ||
The smoothness of a rotor is called rotor finish. It is measured in microinches. The finish classification of microinch means the distance between the highest peak and the deepest valley. The usual method of expressing surface finish is the arithmetic average roughness height or Ra. The higher the Ra, the rougher the surface finish. The lower the Ra, the smoother the surace finish
Machining a Disc Brake Rotor
Before machining any rotor, use a micrometer and measure the thinness of the rotor. Check the specifications for the minimum allowable thickness. Visually check the rotor for evidence of heat cracks or hard spots that would require replacement (rather than machining) of the rotor. After removing the grease seal and bearings, remove the grease from the bearing races. Clean and inspect the brake lathe spindle for damage or burs that could affect its accuracy. Select a tapered cone adapter that fits the inner bearing race. Slide the cone adapter onto the brake lathe spindle. Select the proper size cone adapter for the smaller outer wheel bearing race. Place the rotor onto the large cone adapter and then slide small cone adapter into the outer wheel bearing race. Install the self-aligning spacer (SAS) and spindle nut. Tighten the spindle nut (usually left-Handed threads). If a hub less rotor is being machined, be sure to thoroughly clan the inside surface. Also remove all rust from the other side of the hub less rotor. Select the proper centering cone for the hole in the center of the hub. Select the proper size cone-shaped hub less adapter and tapered centering cone with a spring in between. After sliding the rotor over the centering cone, install the matching hub less adapter. Install the self-aligning spacer (SAS) and spindle nut. After the rotor has been secured to the brake lathe spindle, install the noise silencer band (dampener). Carefully inspect the cutting bits and replace, if necessary. Loosen the holder arm. Adjust the twin cutter arm until the rotor is centered between the two cutting bits. Turn the lathe on. Move the cutter arm toward the center of the rotor, placing the cutting bits in about the center of the friction surface. Turn one cutting bit into the surface of the rotor to make a scratch cut. This step checks the lathe step-up for accuracy. Turn the lathe off. Observe the first scratch cut. Loosen the spindle retaining nut, rotate the rotor 180 degrees (one-half turn) on the spindle of the brake lathe. Tighten the spindle nut. Turn the lathe back on and turn the cutting bit slightly into the rotor until a second scratch cut is made. If the second scratch cut is in the same location as the first cut or extends all around the surface of the rotor, then the rotor is properly installed on the lathe. Start the machining process by moving the twin cutters to about the center of the rotor friction surface. Turn the cutting bits inward until they touch the rotor and zero the depth adjustment. Adjust the twin cutters, then dial in the amount of depth (0.005-0.010 in. per side for a rough cut or 0.002 in. for a finish cut) and lock the adjustment so that vibration will not change the setting. Turn the feed control knob until the desired feed rate is achieved for the first or rough cut (0.006-0.010 in per revolution) or finish cut (0.002 in. per revolution). Engage the automatic feed. Observe the machining operation. After cutting bits have cleared the edge of the rotor, turn the lathe off and measure the thickness of the rotor. Readjust the feed control to a slow rate (0.002in per revolution or less) for the finish cut. Reposition the cutting bits for the finish cut. Loosen the adjustment locks. Turn the depth of the cut for the finish cut (0.002 in. maximum). Lock the adjustment. Engage the automatic feed. Use 150-grit aluminum-oxide sandpaper on a block of wood for 60 seconds per side or a grinder to give a no directional and smooth surface to both sides of the rotor. After the sanding or grinding operation, thoroughly clean the machined surface of the rotor to remove any and all particles of grit that could affect the operation and life of the disc brake pads. Remove the silencer band. Loosen the spindle retaining nut and remove the rotor.
Rough Cut
the first cut when maching a drum or rotor
Finish Cut
final cut of .002 to make the final surface as smooth as possible
NonDirectional Finish- Manufacturers recommend a non directional finish to help prevent the grooves machined into the rotor from acting like grooves on a record, that will force the pads outward on the rotor
Surface Finishing the Rotor
Restoring the braking effectiveness to match new vehicles by getting the surface as smooth or smoother than a new rotor for maximum pad contact
Cleaning Rotors
After machining and sanding the rotors, they should always be cleaned. Brake clean and a rag are better than nothing, but General Motors recommends washing the rotor or drum with warm soapy water and rinsing with clean warm water then drying with compressed air.
On-the-vehicle Rotor Machining
On vehicle machining is necessary for vehicles with “captured rotors” such as the Colorado and Canyon pick-up trucks. Many manufacturers also require the use of on-vehicle lathes to correct brake rotor runout concerns. GM does not recognize the use of on-vehicle lathes to correct such concerns.
- How Brakes Stop Vehicles
- Brakes are an energy-absorbing mechanism that converts vehicle movement into heat while stopping the rotation of the wheels.
- All braking systems are designed to reduce the speed and stop a moving vehicle and to keep it from moving if the vehicle is stationary.
- Drum Brakes
- Drum brakes use friction material called shoes. Drum brakes are not as efficient as disc brakes at dissipating heat. Drum brakes can apply more stopping power for the given amount of force applied to the brake pedal.
- Disc Brakes
- used on the front of most vehicles they operate by squeezing brake pads on both sides of a rotor or disc that is attached to a wheel
- Weight Transfer During Braking
- Inertia in the form of weight transfer plays a major part in braking performance, Newton’s First law of motion states that an object in motion will remain in motion unless acted upon by an outside force. The brakes are that outside force and when braking the wheels and tires slow immediately. The rest of the vehicle attempts to stay in motion, therefore the weight transfers to the front wheels.
- Friction
- friction is the force between two objects in contact with each othe
- Brake Fluid
- Brake fluid is the life source of the braking system. without brake fluid the brakes would not work. since fluid is non compressible, it acts as a hydraulic. brake fluid has a high boiling point since the brakes get to a temperatrure of 1300 degrees F and get as high as 1800 degrees F. brake fluid also has a high freezing point.
- DOT Brake Fluid Specs.
- The Department of Transportation has established brake fluid standards shown in the table.
http://www.shotimes.com/SHO3brakefluid.html- Hydraulic System Mineral Oil
- Some French-built and British designed cars use HSMO (Hydraulic System Mineral Oil) as part of their hydraulic control systems. They use a hydraulic pump to pressurize the HSMO for use in suspension leveling and braking systems.
- Brake Fluid Testing
- Check proper level after inspecting entire brake system for worn pads or shoes and leaks; Check color/condition should be clear or amber; Use test strips for copper ions, compare test strip to color on package;Or, an electronic boiling point tester is submerged into the master cylinder fluid, push the button and the boiling temperature will be displayed. For contamination, fill a styrofoam cup with water, place a teaspoon of brake fluid and it should completely dissolve. Petroleum or mineral oil fluids will float to the surface and retain their color. Contaminated brake fluid must be drained, flushed, and replace all rubber components.
- Brake Fluid Disposal
- Brake fluid should be disposed of just like petroilime based products and not just dumped down the drain or dumped outside.
Brake lining Composition:A molded resin friction material composition for automobiles or the like. This composition contains as base fibers chopped glass fibers and pulped polyamide fibers in a given compounding ratio. This composition enables to produce brake lining having a high friction coefficient, a low wear ratio, and an improved fade. The fade can be further improved by adding cryolite powder and zirconium oxide powder to the composition.
cause serious diseases of the lungs and other organs
that may not appear until years after the exposure has
occurred. For instance, asbestosis can cause a buildup
of scar-like tissue in the lungs and result in loss of lung
function that often progresses to disability and death.
Asbestos fibers associated with these health risks are
too small to be seen with the naked eye, and smokers
are at higher risk of developing some asbestos-related
diseases.